成矿金属元素的气相运移研究进展

尽管早在360余年前就有人提出了金属元素气相运移的概念,但在近代矿床学和矿床地球化学研究中却一直没有予以充分的重视。现代陆上和海底火山喷气中金属元素的分析表明很多金属元素在火山气中的含量相当高,具有直接形成金属矿床的潜力。随着现代分析技术的发展,特别是同步加速器-XRF、PIXE、LAM-ICP-MS等的出现,使得我们可以直接测定流体包裹体的微量元素组成,取得了富气相的流体包体中Au、Cu、Mo等元素的含量显著的高于液相包体的重要发现。熔融包体的研究结果也表明岩浆沸腾作用在热液矿床的成矿过程中可能起着重要的作用,在岩浆的结晶过程中可能有高达65%的挥发份逸出,而Cu、Au等金属元素强烈的选择性进入气相而非熔体相,说明岩浆演化早期的去气过程对斑岩等热液矿床的形成可能具有重要的控制。气相对金属元素溶解度的实验研究亦表明,气相对金属的溶解和迁移能力比人们想象的要高得多。所以,气相运移可能在一些热液矿床(特别是在蒸气相占重要地位的高温热液矿床)的成矿过程中可能起着重要的作用。

VAPOR-TRANSPORT OF ORE METALS: A REVIEW

The idea that vapors can transport metals in appreciable concentrations and may play an important role in the formation of ore deposits was suggested some 360 years ago, however, in the modern era it has been largely ignored. Significant metal concentrations have been reported from volcanic gases worldwide, and the possibility of concentrating directly to form potential ore deposits has been recognized. The development of new micro-analytical techniques, especially the synchrotron XRF, PIXE, LAM-ICP-MS, enables us to measure the concentrations of ore metals in fluid inclusions directly. The results show that metals such as Au, Cu, and Mo, are significantly concentrated in the gas-rich fluid inclusions. Evidences showing that vapor-transport of metals may play a very important role in the formation of hydrothermal deposits also come from the melt-inclusion investigations. During the magma degassing or boiling process, metals such as Cu and Au are preferentially concentrated in vapors rather than melts, while up to 65% of volatiles may be exsolved from the crystallizing magmas. Vapor solubiltiy experiments suggest that the solubilities of metals in the vapor phases are much more significant than were expected. Thus, vapor-transport of metals may play a very important role in the formation of a variety of ore deposit types, particularly the high temperature hydrothermal deposits associated with magmatism where vapor is a major or dominant phase in the hydrothermal system.